When the temperature exceeds 300-400 ° C (blue fragile zone of steel), reaching 700-800 ° C, the deformation resistance will be drastically reduced, and the deformation energy is also greatly improved. According to the forging in different temperature regions, for the forging quality and the forging process requirements, it can be divided into three forming temperature zones: cold forging, warm forging and hot forging. There is no strict limit to the division of such temperature regions. Generally speaking, forging in a temperature region where recrystallization is performed is called hot forging, and forging at room temperature is called cold forging.
In the case of low temperature forging, the dimensional change of the forging is small. Forging at 700 ° C or less, the formation of scale is small, and there is no decarburization on the surface. Therefore, as long as the deformation can be in the forming energy range, cold forging is easy to obtain good dimensional accuracy and surface finish. As long as the temperature and lubrication cooling are controlled, warm forging below 700 °C can also achieve good precision. In hot forging, since the deformation energy and deformation resistance are small, large forgings with complicated shapes can be forged. For high-precision forgings, hot forging can be performed in the temperature range of 900-1000 °C. In addition, attention should be paid to improving the working environment of hot forging. Forging die life (hot forging 2-5 thousand, warm forging 1-2 million, cold forging 2-5 thousand) is shorter than forging in other temperature ranges, but it has a large degree of freedom and low cost .
The billet is deformed and hardened during cold forging, so that the forging die is subjected to high loads. Therefore, it is necessary to use a high-strength forging die and a hard lubricating film treatment method for preventing wear and adhesion. In addition, in order to prevent cracking of the billet, intermediate annealing is performed as needed to ensure the required deformability. In order to maintain a good lubrication state, the billet can be phosphatized. At the time of continuous processing with bar stock and wire rod, the section cannot be lubricated at present, and the possibility of using a phosphating lubrication method is being studied.
According to the movement mode of the blank, the forging can be divided into free forging, upsetting, extrusion, die forging, closed die forging, and closed upsetting. Closed die forging and closed upset forging have high material utilization due to the absence of flash. Finishing of complex forgings is possible with one or several processes. Since there is no flash, the area of ​​force applied to the forging is reduced and the required load is also reduced. However, care should be taken not to completely limit the blank. To this end, the volume of the blank is strictly controlled, the relative position of the forging die is controlled, and the forging is measured to reduce the wear of the forging die.
According to the movement mode of the forging die, forging can be divided into pendulum, pendulum swivel, roll forging, cross wedge rolling, boring ring and cross rolling. Swing, swivel and shackle can also be used for precision forging. In order to improve the utilization of materials, roll forging and cross rolling can be used as a front-end process for slender materials. The same rotary forging as free forging is also partially formed, which has the advantage that it can be formed in the case of a smaller forging force than the forging size. This type of forging, including free forging, expands from the vicinity of the mold surface to the free surface during processing. Therefore, it is difficult to ensure accuracy. Therefore, the movement direction of the forging die and the swaging process can be controlled by computer. The forging force obtains products with complex shapes and high precision. For example, forgings such as steam turbine blades with a large variety and large size are produced.
The die motion and degree of freedom of the forging equipment are inconsistent. According to the characteristics of the bottom dead center deformation, the forging equipment can be divided into the following four forms:
· Limit the form of forging force: the hydraulic press that directly drives the slider.
· Quasi-stroke limit mode: Hydraulic press that drives the crank-link mechanism hydraulically.
· Stroke limiting mode: mechanical presses that drive the slider with cranks, connecting rods and wedge mechanisms.
· Energy limiting method: use the screw and friction press of the screw mechanism.
In order to achieve high accuracy, care should be taken to prevent overload at the bottom dead center, control speed and mold position. Because these will have an impact on forging tolerances, shape accuracy and forging die life. In addition, in order to maintain accuracy, you should also pay attention to adjust the slider rail clearance, ensure the stiffness, adjust the bottom dead center and use the auxiliary transmission and other measures.
In addition, depending on the way the slider moves and the vertical and horizontal movement of the slider (for forging of the elongated part, lubrication cooling and part forging of high-speed production), the compensation device can increase the movement in other directions. Different methods are used, the required forging force, process, material utilization, production, dimensional tolerance and lubrication cooling method are different. These factors are also factors that affect the level of automation.
In the case of low temperature forging, the dimensional change of the forging is small. Forging at 700 ° C or less, the formation of scale is small, and there is no decarburization on the surface. Therefore, as long as the deformation can be in the forming energy range, cold forging is easy to obtain good dimensional accuracy and surface finish. As long as the temperature and lubrication cooling are controlled, warm forging below 700 °C can also achieve good precision. In hot forging, since the deformation energy and deformation resistance are small, large forgings with complicated shapes can be forged. For high-precision forgings, hot forging can be performed in the temperature range of 900-1000 °C. In addition, attention should be paid to improving the working environment of hot forging. Forging die life (hot forging 2-5 thousand, warm forging 1-2 million, cold forging 2-5 thousand) is shorter than forging in other temperature ranges, but it has a large degree of freedom and low cost .
The billet is deformed and hardened during cold forging, so that the forging die is subjected to high loads. Therefore, it is necessary to use a high-strength forging die and a hard lubricating film treatment method for preventing wear and adhesion. In addition, in order to prevent cracking of the billet, intermediate annealing is performed as needed to ensure the required deformability. In order to maintain a good lubrication state, the billet can be phosphatized. At the time of continuous processing with bar stock and wire rod, the section cannot be lubricated at present, and the possibility of using a phosphating lubrication method is being studied.
According to the movement mode of the blank, the forging can be divided into free forging, upsetting, extrusion, die forging, closed die forging, and closed upsetting. Closed die forging and closed upset forging have high material utilization due to the absence of flash. Finishing of complex forgings is possible with one or several processes. Since there is no flash, the area of ​​force applied to the forging is reduced and the required load is also reduced. However, care should be taken not to completely limit the blank. To this end, the volume of the blank is strictly controlled, the relative position of the forging die is controlled, and the forging is measured to reduce the wear of the forging die.
According to the movement mode of the forging die, forging can be divided into pendulum, pendulum swivel, roll forging, cross wedge rolling, boring ring and cross rolling. Swing, swivel and shackle can also be used for precision forging. In order to improve the utilization of materials, roll forging and cross rolling can be used as a front-end process for slender materials. The same rotary forging as free forging is also partially formed, which has the advantage that it can be formed in the case of a smaller forging force than the forging size. This type of forging, including free forging, expands from the vicinity of the mold surface to the free surface during processing. Therefore, it is difficult to ensure accuracy. Therefore, the movement direction of the forging die and the swaging process can be controlled by computer. The forging force obtains products with complex shapes and high precision. For example, forgings such as steam turbine blades with a large variety and large size are produced.
The die motion and degree of freedom of the forging equipment are inconsistent. According to the characteristics of the bottom dead center deformation, the forging equipment can be divided into the following four forms:
· Limit the form of forging force: the hydraulic press that directly drives the slider.
· Quasi-stroke limit mode: Hydraulic press that drives the crank-link mechanism hydraulically.
· Stroke limiting mode: mechanical presses that drive the slider with cranks, connecting rods and wedge mechanisms.
· Energy limiting method: use the screw and friction press of the screw mechanism.
In order to achieve high accuracy, care should be taken to prevent overload at the bottom dead center, control speed and mold position. Because these will have an impact on forging tolerances, shape accuracy and forging die life. In addition, in order to maintain accuracy, you should also pay attention to adjust the slider rail clearance, ensure the stiffness, adjust the bottom dead center and use the auxiliary transmission and other measures.
In addition, depending on the way the slider moves and the vertical and horizontal movement of the slider (for forging of the elongated part, lubrication cooling and part forging of high-speed production), the compensation device can increase the movement in other directions. Different methods are used, the required forging force, process, material utilization, production, dimensional tolerance and lubrication cooling method are different. These factors are also factors that affect the level of automation.
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